In spite of the importance of cell motility for many cellular functions, including mitosis, phagocytosis, cell migration, intracellular transport and embryological development, the molecular mechanism of biological motility remains one of the major unanswered questions in cell biology. The objective of the proposed research is to learn how cells generate and control the forces that make them move. First, the biochemistry and ultrastructure of purified contractile proteins - actin, myosin and associated proteins - from both an ameba and from human platelets will be studied in detail. Then these proteins will be localized in intact motile cells by correlation of light and electron microscopic observations and their positions in the cell related to the typical movements of the cell. Finally, experiments are planned which may prove the relationship between the purified contractile proteins and cellular movements: fractionation and recombination experiments on motile cell-free extracts from amebas and the isolation and characterization of temperature sensitive non-motile mutants of Acanthamoeba.